The present invention is directed to an electron bombarded semiconductor device and more specifically to an improved amplifier of the above type with an inverted class B output circuit.
A conventional class B electron bombarded semiconductor (EBS) amplifier is illustrated schematically in FIG. 1 and in U.S. Pat. No. 3,749,961 assigned to the present assignee. The diodes D1 and D2 are illuminated during alternate halves of a radio frequency (RF) cycle by a deflected electron beam which is generated as shown in the above patent. By causing the addition of two half sine waves in the common output line there is formed a sinusoidal output voltage across the load Z.sub.L. This load is of a 50 ohm impedance level and it is matched with the output signal at the common junction of the diodes by a impedance transformer network and a bandshaping network. RF choke coils are also provided in series with the battery sources.
The diodes are reverse biased by the respective dc voltage sources V.sub.cc which are tied together at ground, which is also the other terminal of the load Z.sub.L and a common connection for a pair of bypass capacitors C.sub.B. These bypass capacitors provide a return path to ground for the radio frequency current flowing in the diodes, while blocking the dc bias supply currents. It is necessary that these capacitors be located physically close to the diodes in order to minimize effects due to propagation time which would lead to partial cancellation of the RF signal. The bypass capacitors also function in concert with the RF chokes to prevent radio frequency voltages from entering the dc bias supplies.
Thus, it is apparent that the bypass capacitors C.sub.B are required to accomplish many functions some of which are antithetical in nature.
To summarize the operation of an EBS circuit as set out in FIG. 1, during the quiescent position of the beam it impinges between the diode targets of D1 and D2 and no current flows in either diode. Deflection of the beam to the upper diode causes current to flow so that a positive polarity voltage is developed; deflecting the beam to the other target causes an opposite polarity. Current flowing in the diodes at any instant of time is proportional to the area of the diode which is illuminated by the beam. The diode and beam geometry is designed so that there exists a linear relationship between beam deflection and the output voltage generated across the load Z.sub.L. The class B operation described above is advantageous in providing high efficiency linearity, and broad band frequency response.